小兴安岭-张广才岭地区晚古生代至中生代花岗岩的成因及其地质意义

Petrogenesis of the Late Paleozoic to Mesozoic granite from the Xiao Hinggan Mountains-Zhangguangcai Mountains and its geological implications

中国东北地区显生宙花岗岩的成因一直是中亚造山带东段研究的热点之一,尤其是小兴安岭-张广才岭地区的花岗岩其成因及形成的大地构造背景一直存在较大争议。本文新获得小兴安岭-张广才岭铁力和依兰地区的二长花岗岩LA-ICP-MS锆石U-Pb年龄分别为188±1 Ma和257±3 Ma。地球化学数据显示,两地区的二长花岗岩均为Ⅰ型花岗岩并且富集大离子亲石元素(Th和U等)和轻稀土元素,亏损高场强元素(Nb和Ta等)和重稀土元素具有弧岩浆岩的地球化学特征。锆石Hf同位素数据显示,铁力地区二长花岗岩的岩浆源区可能来自于中新元古代的下地壳部分熔融。综合前人在小兴安岭-张广才岭地区已发表的花岗岩类岩石的地质年代学和地球化学数据,初步推测小兴安岭-张广才岭地区在晚古生代至中生代期间处于活动大陆边缘环境。同时,小兴安岭-张广才岭地区晚古生代至中生代的岩浆岩具有自东向西形成时代逐渐变年轻的趋势,这可能是由于东侧的牡丹江洋在晚古生代至中生代期间俯冲角度逐渐变缓造成的。

Extensive Phanerozoic granitoids in northeastern China have constituted one of the hotspots in the study of granite in the eastern Central Asian Orogenic Belt.In particular,the petrogenesis and tectonic affinity of granites in the Xiao Hinggan Mountains-Zhangguangcai Mountains have always been controversial.In this study,zircon LAICP-MS U-Pb dating of the monzogranites from the Tieli and Yilan areas in the Xiao Hinggan MountainsZhangguangcai Mountains yielded crystallization ages of 188±1 Ma and 257±3 Ma,respectively.The geochemical data show that these monzogranites belong toⅠ-type granite and are characterized by enrichment of LILE(e.g.,Th and U)and LREE and depletion of HFSE(e.g.,Nb and Ta)and HREE,which are typical for continental arc-type granites.Zircon Hf isotopic data indicate that the granitic magma in the Tieli area was derived from partial melting of Meso-to Neoproterozoic lower crust.Combined with previously published geochronological and geochemical data,it is inferred that the Xiao Hinggan Mountains-Zhangguangcai Mountains was under an active continental margin setting during the Late Paleozoic to Mesozoic.Moreover,the Late Paleozoic to Mesozoic granitoids show a westward increasingly younger trend in the whole Xiao Hinggan Mountains-Zhangguangcai Mountains.The authors hold that this temporal and spatial relationship resulted from the flattening westward subduction of the Mudanjiang Ocean between the Jiamusi and Songnen blocks.